This invention relates generally to a lifting device such as a forklift, and more particularly to an attachment for a lifting device having a variable reach.
A typical so-called variable reach forklift has a boom pivotally attached to the vehicle at one end and a fork carriage with a pair of lifting tines fixed to the other end of the boom. The boom may be rotated about its pivot to change the vertical height of the fork carriage and lifting tines, as desired. Additionally, the boom preferably comprises at least a pair of telescoped segments to permit lateral extension and retraction of the fork carriage and lifting tines. The extension and retraction of the carriage occurs only in-line with the telescoped segments of the boom. Accordingly, when the boom is rotated about its pivot to raise the carriage, the carriage is only extendable along this inclined angle corresponding to the inclination of the boom.
In many instances, it is desirable to not only raise the carriage to a desired height, but to thereafter advance the carriage substantially horizontally to a reference such as the ground or the horizon. By way of example, it may be desirable to raise the fork carriage by pivoting and inclining the boom and thereafter advancing the fork carriage through, for example, an opening and scaffolding or through an open window of a building, to place an object or objects on the lifting tines on the scaffolding or in the building. It is desirable to provide this movement without having to move the entire vehicle.
Still further, there is a need for an apparatus which increases the range of movement of the fork carriage beyond that attainable by the boom and permits movement of the fork carriage along a path not coincident or parallel to the axis of the boom. Further, throughout the movement of the fork carriage, it is desirable that the lifting tines maintain a desired orientation to facilitate balancing and carrying objects on the lifting tines. Prior lift trucks have utilized a separate hydraulic cylinder operably connected to the fork carriage and either automatically or manually operated to maintain the desired orientation of the lifting tines.
A variable reach device for attachment to a boom of a lift truck to increase the rang e of movement of a fork carriage o f the lift truck. In one embodiment, the device has a mast connected at one end to the boom and an arm pivotally connected at one end to the other end of the mast with the fork carriage pivotally connected to the other end of the arm. The arm pivots about the mast in one direction to fold or retract the device and dispose the fork carriage in its retracted position. The arm pivots about the mast in a second direction to unfold or extend the device and move the fork carriage away from the boom along an arcuate path having both vertical and horizontal components. In another embodiment, the reach device provides a purely horizontal movement of the fork carriage to extend the fork carriage away from the boom as the device unfolds and to retract the fork carriage back towards the boom as the device is folded. In this embodiment, the fork carriage is slidably carried by the arm via a lift chain connected to a cam which rotates in proportion to the rotational movement of the arm relative to the mast. The cam is designed to let out or take up the lift chain in proportion to the vertical component of the movement of the free end of the arm as it pivots about the mast to maintain the constant vertical height of the fork carriage as it is laterally advanced and retracted.
Desirably, in both embodiments of the reach device, the inclination or attitude of the lifting tines of the fork carriage is maintained throughout the range of movement of the fork carriage. This is accomplished by operably connecting the fork carriage to a sprocket driven through a chain by a drive sprocket which rotates in response to and in proportion to the pivotal or rotational movement of the arm about the mast.
Objects, features and advantages of this invention include providing a reach device for a fork lift which increases the range of movement of a fork carriage, maintains lifting tines of the fork carriage in a desired orientation throughout the range of movement of the fork carriage, can provide a purely horizontal advancement of the fork carriage relative to the boom, can provide both an increased vertical and an increased horizontal reach relative to the boom, utilizes a single hydraulic cylinder to both the advance the fork carriage and to maintain its lifting tines level, increases the utility of the fork lift, permits increased advancement of the fork carriage without moving the forklift vehicle, is of relatively simple design and economical manufacture and assembly, is reliable, durable and has a long, useful life in service.